Well perforating method



June 30 1970 G; o. suMAN, JR 3,51'IVJ-` WELL PERFORATING METHOD Filed June 20, 1968 2 Sheets-Sheet 1 INVENTORI GEORGE O. SUMAM', JR. av/:yew

HIS ATTORNEY June 30, 1970 G. o. suMAN, JR

WELL PERFORATING METHOD 2 Sheets-Sheet 2 Filed June .20, 1968 I TREATMENT EQUIPMENT PERFRATED INTERVAL DIESEL on.`

SUPER .MUD ACID FIG. 2

INVENTORI GEORGE o. suMAN',"JR. away f Has ATTORNEY 3,517,745 WELL PERFORA'I'ING METHOD George 0. Snman, Jr., Metairie, La., assignor to Shell Oil Company, New York, N.Y., a corporation of Dela- Ware Filed June 20, 1968, Ser. No. 738,530 Int. Cl. E21b 43/25 U.S. Cl. 166-297 6 Claims ABSTRACT F THE DISCLOSURE A method of perforating a well casing extending into communication with a subterranean hydrocarbon-bearing formation having an interval portion adjacent the formation by introducing a uid into a restricted zone of the Well casing and adjacent the interval portion under controlled pressure conditions raising the pressure of the uid to a pressure at least suiicient to drive the fluid out of the well casing and into the formation upon perforation of the casing and perforating the casing and adjacent interval portion so as to force the fluid through the established perforations and into the hydrocarbon-bearing portion of the formation.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method for producing perforations in solid materials and more particularly to a method for creating such perforations in wells and earth formations penetrated by a well borehole.

Description of the prior art In many types of wells, such as oil or gas Wells, for example, a casing is placed in the well borehole, and the casing is then perforated in the vicinity of selected producing zones in the surrounding earth formation to thereby condition the well for production operations. In the forming of such perforations, the resulting cavities desirably extent not only through the well casing but also through the surrounding cement and a portion of the ad-y jacent earth formation. As an illustration, it often is advantageous to fracture the earth formation adjacent the producing zones, such as by hydraulic means, for example, in order to increase the permeability of the formation, and the cavities greatly facilitate the fracturing operation.

Various methods and apparatus have been used heretofore in the perforation of a fwell casing and/or a selected earth formation in a well borehole. Thus, in some cases, the perforations have been produced mechanically and have also been formed through the use of explosive means, such as a jet or bullet perforating gun.

Prior to perforating a casing or formation with suitable devices, e.g., guns, a sheath is placed around the casing. This may be a cement sheath or formation material surrounding the well borehole and particularly around the part to be perforated. These materials pulverized by the perforating device consist of sand, clay, cement, limestone, dolomite, etc. in conjunction with mud particles and/or clay dispersed by mud or cement filtrate, which are believed to plug the perforations. These materials subsequently cause plugging of the formation which materials must be removed prior to conducting other completion operations and/ or placing the well on production. This is a relatively time-consuming and expensive process.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved method for perforating well formations.

tat-es Patent O" 3,517,745 Patented June 30, 1970 It is a further object of this invention to perforate well formations while maintaining well control from the time of perforating to conducting subsequent operations with solids-free fluids in the well.

It is a still further object of this invention to providea well perforating method in which substantially all of the perforation-plugging agents generally surrounding the areas being perforated are removed by high pressure flushing and/or chemical means during the perforating step.

These objects are preferably carried out by introducing a fluid under controlled pressure through the well into a subterranean hydrocarbon-bearing formation opposite and adjacent the interval to be perforated, The fluid is preferably adapted to remove at least some of the plugging material in the interval portion of the formation. A perforating device is lowered into the interval portion and the pressure of the fluid is raised to a pressure at least sufficient to drive the fluid out of the well and into the formation. Not only is the interval portion perforated, but the pressurized fluid is driven out of the well through the perforations while removing some or all of the mpairment material surrounding the perforations.

BRIEF DESCRIPTION OF THE DRAWINGS EIG. 1 is a vertical sectional view of a preferred method for carrying out the concepts of the invention; and

FIG. 2 is a vertical sectional, partly schematic view of an example of the method of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, there is shown a well bore-hole 11 extending through overlying earth formation 12 into communiction with a s-ubterranean hydrocarbon-bearing formation 13. The hydrocarbon-bearing production zone is confined by lower layer 12a. Well borehole 11 is preferably cased at casing 14 and cemented at 15 as is well known in the art. Casing 14 is closed at its upper end -16 and preferably includes a tubing string 17 extending therethrough into engagement with 13. Tubing string 17, however, is not necessary for carrying out the teachings of this invention. A fluid inlet 18, disposed at the upper end of casing 14, communicates with both an external iiuid source (not shown) and the interior of well borehole 11.

A perforating device 19 is illustrated in FIG. 1 as having been lowered, through suitable lowering means, such as a winch (not shown) and a cable 20, through tubing string 17 into well borehole 11. Besides being of suicient strength to raise and lower perforating device 19 in well borehole 11, cable 20 may include the necessary electrical, mechanical or hydraulic conduits for actuating device 19. Perforating device 19 may be any suitable penetrating means, such as a jet or bullet perforator as is well known in the art. Perforators are generally of two types, both lowered into the well borehole on conductor cables and carrying explosive charges that are electrically detonated. In the bullet perforator, steel bullets are fired through the casing and cement; in the shaped charge perforator, small explosive charges are used, so shaped that the explosive force is focused and intensified into a small diameter jet which penetrates casing and cement.

In operation, an acid or other dissolving and/or chemically reactive fluid is preferably pumped into well/borehole 11 through iluid inlet 18 or down tubing 17 above the formation 13 and surrounding the interval portion of well borehole 11 which interval portion includes the portions of casing 14, cement 15 and formation 131 desired to be perforated. This fluid is adapted to dissolve and/or react with the material comprising the material of formation 13 and the interval material (that is, the

material comprising the cemented casing, etc.) or portions thereof. When used throughout the remainder of this specification, the fluid referred to, unless otherwise indicated, is a Huid adapted to remove the interval and formation materials (referred to as impairment material). The word dissolve or dissolves as used throughout this specification includes any chemical reaction or reactions adapted to break down or decompose materials such as various types of mud acids (Le.) solutions of hydrochloric and hydrofluoric acids).

The pressure of the fluid is then raised, as by pumping from the surface through inlet 18, So as to drive the fluid out through all of the perforations 21 when the perforating device 19 is actuated. Obviously, the number of perforations 21 depends on the extent of the interval to be perforated. The pressure of the fluid is raised to previously determined or estimated over-balance pressures which may, but not necessarily, lbe capable of fracturing the perforated material (i.e., the perforated formation 13). The surface pressure of the iud is thus raised and controlled by means well known in the art to provide an instantaneous surge of the active fluid into all perforations 21 at high differential pressures. An important feature of this application is considered to be the magnitude of the differential pressures involved. For maximum capability of forcing fluid into each perforation, the highest possible differential pressures are desired, limited only by mechanical equipment in use and pressures at which cement bonding can be destroyed or fractures generated (if fractures are not desired for the completion being effected). The use of relatively high surface pressures during the perforating operation is therefore a key to this procedure.

By perforating in the presence of such relatively high differential pressures and with the fluid in the well bore capable of removing the impairment material (i.e., the pulverized materials plugging the perforations 21 and any other material surrounding the perforations 21), such plugging is reduced and/or substantially eliminated. The driving force of the fluid assures that suflicient fluid is driven into all the perforations; regardless of the restrictions to flow imposed 'by the plugging agents and/or normal permeability variations, thereby causing substantial removal of the plugging agents from most and/or all perforations. lf the fluid is not adapted to dissolve such impairment material, the fluid is introduced at sufficiently high enough pressure to remove or flush such material away from the borehole 11.

Since the step of perforating can be conducted through a tubing string as discussed hereinabove, well control can be maintained from the step of perforating through any necessary subsequent steps.

For example, with the tubing string 17 in place, after perforating, the perforating device 19 is removed and resin or plastic consolidation materials are pumped down the well through tubing string 17 and out through the perforations 21 thereby consolidating the sand of formation 13. In poorly consolidated sand formations, sand may be carried into the well borehole with the oil and gas. This should be prevented, or at least kept to a minimum, to avoid plugging the well thereby stopping production `and to lessen the wear of pumps, valves, liners, etc. The production of large quantities of sand alone or in combination with reservoir compaction can also cause damage to the casing of a well through casing deflection or buckling This loose sand may be consolidated by means of binding the sand grains without materially affecting the productivity of a well. Such plastic or resin consolidation ymaterials and methods of consolidation include the epoxy resins manufactured Aby Shell Chemical Co. and the consolidation method described in U.S. Pats. 3,368,625; 3,368,626; and 3,339,633. Other types include phenol-formaldehyde resins and silicates etc. If sand exclusion is delayed until the formation has been disturbed by fluid movement or other factors, sand consolidation becomes more difficult and, in some cases, impossible. -Trace amounts of solids in any of the pretreating fluids can prevent resins or plastics from entering one or more of the perforations, thus resulting in an unsuccessful treatment. As the perforating in accordance with the method of this invention is carried out in a clean fluid, it can be seen that the success of any subsequent sand consolidation treatment is greatly enhanced by this degree of cleanliness maintained in the well from the time of perforating through the time of plastic or resin placement in the unconsolidated formation.

Since the fluids present in the well utilizing the method of this invention and which would precede any well treatment following perforating are solid-free, no plugging occurs. Thus, from operation to operation, there is no plugging of the cleaned-out perforations 21. Following sand consolidation or other treatments in which the need for unplugged perforations is imperative, fluids containing solids for fluid loss control (.and/ or suitable emulsions) may be injected through inlet 18, into the annulus formed between tubing string 17 and casing 14 and well control maintained for later operations. Alternatively, the fluid loss control fluids and/ or emulsions may be injected down tubing string 17 and into well borehole 11.

As disclosed hereinabove, once the casing and formation has been perfor-ated by the method of this invention, placement of plastic consolidation materials for control of sand is facilitated as well as making it possible for proper placement of cement during squeeze operations, open perforations prior to fracturing operations are ensured, more uniform distribution of stimulation treatments are assured and other well completion and worko-ver operations are also made possible. For example, if some perforations are plugged, cement used in squeezing may not go out through them. In this case, a portion of the interval may not receive squeeze cement and a weakness in the job results. If some perforations are plugged, portions of the material will not be fractured nor otherwise stimulated.

EXAMPLE The following is an example of through tubing perforating using a super mud 4acid mixture with a high overbalance pressure in a subterranean earth formation, followed immediately by a plastic consolidation treatment in accordance with the teachings of this invention and as described in the U.S. Pat. 3,339,633.

Overbalance perforating through tubing with acid spotted in the casing opposite the interval to be perforated and with high pressure imposed at the surface was conducted in a well. A surface pressure of 2,000 p.s.i. provided a 5150 p.s.i. bottom-hole pressure and a 3365 p.s..i. overbalance to drive the super mud acid out through all the perforations and into the reservoir (1785 p.s.i. static reservoir pressure). The formation was treated with epoxy resin as described in Example 1 of the above patent by conducting it through the tubing as placed for the perforating operation. See FIG. 2 where a well borehole 22 is shown having a casing 23 and tubing string 24 disposed therein. A wireline 25 extends through tubing 25 and includes a through tubing perforating gun 25a at its lower end. Gun 25a is of the carrier type side-kicked and is actuated forming perforations 21a.

At the time of tiring, the tubing was full of diesel oil with the exception of several hundred feet of super mud acid at the bottom. Thus, the impairment problems associated with solids in the completion fluid were avoided. After retrieving the gun 25a (a 111/16-in. Jet Research Company Sidewinder gun), the epoxy resin composition for earth formation consolidation treatment was conducted immediately without moving the squeeze packer which was in the proper position for the epoxy resin treatment at the time of perforating. Injectivity was established with the diesel oil already in the tubing at 1 b.p.m. at 1300 p.s.i. surface pressure. A portion of the epoxy resin treatment was conducted on a vacuum due to a minor delay. Impairment appears to have been minimized as a result of the technique, and there has been no indication of sand production to date. Currently, the T sand is gas-lifting at daily rates in excess of 425 barrels of tluid with a water cut of 2 percent.

I claim as my invention:

1. A method of perforating a well extending into a subterranean hydrocarbon-bearing formation adjacent an interval portion thereof comprising the steps of introducing a ud under controlled pressure into the well adjacent said interval portion thereof, said fluid -being adapted to remove at least some of the material in said formation interval portion;

lowering a perforating device into said uid in said well adjacent said formation interval portion desired to be perforated; raising the pressure of said fluid to a pressure at least suilicient to drive said fluid out of said well and into said formation interval portion upon perforation but insuicient to fracture said formation; and

perforating said formation interval portion via said perforating device to remove at least some of the impairment material surrounding said perforations by driving said pressurized iiuid out of the well through the perforations formed in said formation interval formation by said perforating device without fracturing said formation interval portion.

2. The method of claim 1 including the step of extending a tubing string into said wel] prior to introducing said uid therein thereby forming an annulus between said string and said well; and introducing said uid into the well through said tubing string.

3, The method of claim 2 including the step of injecting a uid loss control uid down the annulus formed between said tubing string and said well behind said removal iluid.

4. The method of claim 1 wherein the step of introducing a uid adapted to remove at least some of the material in said formation interval portion includes the step of introducing a iluid adapted to subsequently chemically react with said impairment material to thereby dissolve said impairment material.

5. The method of claim 1 including the step of injecting a uid loss control iluid down said well behind said removal iluid.

6.v The method of claim 1 including the step of injecting sand consolidating materials into said well adapted to consolidate any loose sand Within the formation interval portion adjacent said perforations.

References Cited UNITED STATES PATENTS 3,347,315 10/ 1967 Lanmon 166--42 X 2,718,264 9/ 1955 Allen et al. 166-23 2,766,828 10/1956 =Rachford 166-42.1 X 2,832,415 4/1958 Reistle 166-35 X 2,839,142 6/1958 Huber 166--35 2,876,843 3/ 1959 Huber 175-456 3,011,551 12/1961 Young et al 166-35 X 3,066,736 12/ 1962 Venghiattis 16642.1 X 3,170,517 2/ 1965 Graham et al. 166-42.1 3,195,631 7/1965 Smith 166-35 3,198,268 8/1965 Lindblom et al. 166-42.1 X 3,343,600 9/ 1967 Phansalkar et al 166-33 CHARLES OCONNELL, Primary Examiner A. CALVERT, Assistant Examiner U.S. Cl. XJR. 166-305 

